While changing our own behaviour is a great place to start, ultimately we need BIG changes to make a big difference.
This includes grassroots & community initiatives, government legislation changes, improved design by companies, and extended producer responsibility (businesses have to take back their own waste like plastic bottles).
Find a local group or campaign to get behind, and if it doesn't exist then start your own!
Community
There's a lot of great initiatives that already exist that you can get involved in - set up your own group to sew reusable bags, or join a local cleanup group.